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  • Author: Luc Martin x
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Franck Quaine, Luc Martin and Jean-Pierre Blanchi

This manuscript describes three-dimensional force data collected during postural shifts performed by individuals simulating rock-climbing skills. Starting from a quadrupedal vertical posture, 6 expert climbers had to release their right-hand holds and maintain the tripedal posture for a few seconds. The vertical and contact forces (lateral and anteroposterior forces) applied on the holds were analyzed in two positions: an “imposed” position (the trunk far from the supporting wall) and an “optimized” position (the trunk close to the wall and lower contact forces at the holds). The tripedal postures performed in the two positions were achieved by the same pattern of vertical and contact forces exerted by the limbs on the holds. In the optimized position, the transfer of the forces was less extensive than in the imposed position, so that the forces were exerted primarily on the ipsilateral hold. Moreover, a link between the contact force values and the couple due to body weight with respect to the feet was shown.

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Nicolas Termoz, Luc Martin and François Prince

The aim of this study was to assess postural response efficiency to a self-initiated perturbation using an original method based on the inverted pendulum model. Eight young subjects were asked to perform bilateral arm raising and lowering at 3 different speeds while standing on a force plate. The time necessary to recover a steady state following the movement was computed by analyzing the time evolution of the coefficient of determination between the center of pressure and center of mass difference variable (COP-COM) and the horizontal acceleration of the COM. Results show a spatial reorganization (hip strategy) of the segments following the perturbation and a strong influence of the linear relationship to the arm velocity. However, the conditions of arm velocity did not have any effect on the time response of the postural control, suggesting that this parameter would be an invariant characteristic of the movement. These results support the existence of an internal representation of the inertial constraints related to the movement execution.